Since the Rasbperry Pi is often mentioned in the stream as a potential "minimal hardware" platform for the game, I thought it might be interesting to bring up the latest news... a new version of the RPi has been released with significant upgrades to CPU and memory:

Yeah Microsoft has said that Windows 10 for Pi will be VERY pared down (part of their Internet of Things platform). If it has a UI at all, it will be very minimal. Probably best to keep the Raspberry Pi port as a linux port. Fewer layers of O/S cruft to get in the way!

As for RPi port - I don't think that is same as Linux port. Of course you'll be able to run Linux port more or less directly on RPi. Just install your favorite distribution and compile HH with compiler that supports ARM linux target (and hope Linux port won't depend on x86 intrinsics).

Yes, or RPi (or RPi2) port will use nothing at all besides the "fixed" boot loader that is undocumented (and thus we can't replace it). But there will be no operating system running, just Handmade Hero!

Small in terms that it is pretty readable. You can start reading it without being totally lost. Compare for example how much source you need to read to get some understanding from Linux kernel (without previous experience with that codebase).

Sure, I expect HH RPi usb stack will be a lot smaller. That uspi is a library, it offers at lot of things that won't be needed for HH and can be removed reducing code size. For example, compare size of libSDL windows video module to size of win32_handmade.cpp file.

I'm not an expert on RPi, but I expect sound and graphics doesn't require usb stack :) That's a different code.